This invention relates generally to apparatus employing photocathodes and, more particularly, to an upconverter which allows operation of such apparatus beyond the normal cut-off of the cathode, thereby making possible processing of relatively long wavelength infrared light.
Sensitivity, that is, the ability to develop useful information from weak signals, is a desirable characteristic of photocathode devices, such as photomultipliers and image intensifiers. However, prior art photocathode devices display rapidly decreasing spectral sensitivity at longer wavelengths, culminating in a complete cut-off at wavelengths beyond 1 micron. An example of this is found in night vision equipment which can sense and provide an image of a target weakly illuminated by ambient or by a conventional infrared searchlight but which cannot "see," or may even be damaged by, incident infrared laser light above 1 micron wavelength.
It is therefore an important object of this invention to provide photodetection apparatus which is highly sensitive to infrared radiation and thereby capable of providing useful information regarding longer wavelength infrared images.
A more general object of the invention is to provide new and improved apparatus for use in the infrared.
A more specific object of the invention is to provide night vision equipment having sensitivity to infrared signals arising from various sources.